The present invention relates to a fluid regulator, and more particularly to a fluid regulator of the non-bleed type in which no fluid pressure should be released to atmosphere, such as a fluid regulator capable of regulating the pressure of a fluid such as an oxygen gas in proportion to an electric signal applied and producing the regulated fluid pressure as an output pressure.
Fluid regulators comprising an electropneumatic transducer and a pressure converter in combination have widely been used heretofore for regulating a fluid output pressure to a constant level through the use of an electric signal. One such conventional fluid regulator is shown in FIGS. 1 and 2 of the accompanying drawings.
As illustrated in FIG. 1, an electropneumatic transducer 2 for converting an electric signal to a pneumatic pressure signal has an output connected to a first port 6 of a pressure converter 4 having a diaphragm 8 housed therein. The pressure converter 4 also has a regulator valve 10 having one end held against the diaphragm 8 and the opposite end positioned in a valve hole 15 defined between a second port 12 serving as a pressure supply port and a third port 14 serving as a pressure outlet port for producing an output fluid pressure. Therefore, the pressure converter 4 is of the non-bleed type in which no pneumatic pressure is relieved to atmosphere.
FIG. 2 shows specific details of the electropneumatic transducer 2. The electropneumatic transducer 2 has a torque motor 16 comprising a coil 18 through which extends a balancer beam 22 supported centrally by a pivot 20. A feedback coil spring 24 is attached at one end to one end of the balancer beam 22. The other end of the feedback coil spring 24 is attached to a feedback lever 26 pivotally supported at one end and pressed at its intermediate portion by a feedback bellows 28. The other end of the balancer beam 22 is positioned closely to a nozzle 34 which is supplied with air under given pressure from an air pressure source 30 through a fixed restriction 32. The output air pressure from the nozzle 34 is led to a pilot valve 36 which generates an output air pressure that is regulated by air branched from the air pressure source 30. The output air pressure from the pilot valve 36 is branched to the feedback bellows 28. The torque motor 16 has a magnet 38 disposed around the coil 18 connected to conductors 40 through which an electric input signal is supplied to the coil 18.
When the intput electric signal supplied via the conductors 40 varies, such a signal change causes a change in the electric current flowing through the coil 18, which then causes a change in the magnetic flux generated thereby. The magnetic force acting on the balancer beam 22 is then varied to cause the balancer beam 22 supported on the pivot 20 to turn, thereby varying the distance between the nozzle 34 and the corresponding end of the balancer beam 22. Therefore, the back pressure of the nozzle 34 is also changed. The nozzle back pressure is amplified by the pilot valve 36 into an output air pressure. Part of the output air pressure from the pilot valve 36 is applied to the feedback bellows 28 to push the feedback lever 26. The feedback lever 26 is thus angularly displaced to pull the feedback spring 24, which then angularly displaces the balancer beam 22 to change the nozzle back pressure again. Specifically, the spring 24 acts to cancel out the force tending to displace the balancer beam 22 in response to the electric input signal applied to the coil 18. The balancer beam 22 is brought into equilibrium or a state of balance when the force produced on the balancer beam 22 in response to the electric input signal is equal to the force produced on the balancer beam 22 by the feedback bellows 28. Therefore, the output air pressure can be produced from the pilot valve 36 always in proportion to the electric input signal applied.
It can be understood from the above description that the conventional regulator is basically composed of a mechanism for converting an electric input signal to an air pressure and a mechanism for regulating a fluid pressure in proportion to the converted air pressure. Where a nozzle flapper mechanism is utilized, it is generally possible to construct the electropneumatic transducer with high accuracy since the nozzle back pressure can be regulated highly accurately. However, it would be difficult to incorporate a nozzle flapper mechanism in the pressure converter coupled to the highly accurate electropneumatic transducer because a gas such as of oxygen could not be discharged as an output pressure to atmosphere. Accordingly, it has been customary to use, in combination, a highly accurate electropneumatic transducer and a pressure converter which is not so accurate. The prior fluid regulator is therefore disadvantageous in that its accuracy cannot be increased to a desired level.